D.c. discharge gas laser with novel discharge tube

ABSTRACT

A gas laser comprises a capillary tube and an external tube in which a gaseous lasing medium, such as carbon dioxide gas, is enclosed. Plasma for laser action is generated in the capillary tube by a D.C. discharge between an anode and a cathode. The length of the capillary tube and its relation to the electrodes is such that the plasma area is in said tube.

United States Patent 121 Henrni et a1.

[ 1).C. DISCHARGE GAS LASER WITH NOVEL DISCHARGE TUBE [76] Inventors:Noboru Henmi, 2-3, Midori-machi; Hirqmi Kumagai, 3-4-6 Nishikubo, bothof Musashino-shi, Tokyo, Japan [22] Filed: Aug. 25, 1971 21 Appl. No.:174,604

[30] Foreign Application Priority Data Sept. 5, 1970 Japan 45-78032 [52]U.S. Cl. 331/945 [51] Int. Cl. H015 3/02 [58] Field of Search 331/945[56] References Cited UNITED STATES PATENTS 3,614,654 10/1971 Gronros etal 331/945 Dec. 25, 1973 3,626,325 12/1971 Smith 331/945 3,628,17612/1971 Medicus. 3,466,567 9/1969 Neuscl 331/945 FOREIGN PATENTS ORAPPLICATIONS 1,347,722 11/1963 France 331/945 Primary Examiner-WilliamL. Sikes Attorney lohn M. Webb [57] ABSTRACT A gas laser comprises acapillary tube and an external tube in which a gaseous lasing medium,such as carbon dioxide gas, is enclosed. Plasma for laser action isgenerated in the capillary tube by a DC. discharge between an anode anda cathode. The length of the capillary tube and its relation to theelectrodes is such that the plasma area is in said tube.

4 Claims, 3 Drawing Figures PATENIEUHE025 .915

SHEET 1 OF 2 v VIIII/I/l/IA D.C. DISCHARGE GAS LASER WITH NOVELDISCHARGE TUBE This invention relates to a gas laser, specifically along life gas laser.

In a D.C. discharge gas laser, when a discharge is maintained in adischarge tube, the gaseous medium enclosed in said tube is ionized andthe ionized gas particles are attracted to a cathode by electro-phoresisand absorbed. Consequently, the gas density in the discharge tube is notuniform throughout the full length of the tube with the result that thelaser output decreases. Further, since the discharge tube is heated bythe discharge, the gaseous medium in the tube passes through the wall ofthe tube causing a curtailment in the life of the D.C. discharge gaslaser.

Briefly, according to this invention, a gas laser tube comprises acapillary tube and an external tube in which a gaseous medium, such ascarbon dioxide gas, is enclosed. Both tubes are preferably coaxiallyarranged. At least a portion of the capillary tube is spaced about thelasing axis. Plasma for laser action is generated in the capillary tubeby a D.C. discharge between two electrodes; i.e., an anode and acathode. The length of the capillary tube is longer than the plasma areaor the path of the D.C. discharge within the capillary tube.

The capillary tube has spaced openings, preferably near the cathode andanode. The ionizcdgas particles reaching the cathode are neutralized andthen returned to the anode via the spaced openings and the externaltube.

In this way, the local pressure of the tubes is kept constant and thelife of the gas laser is not curtailed.

Therefore, it is an advantage of this invention to provide a long lifegas laser. Another advantage of this invention is to provide a gas laserof high stability.

Various other objects and advantages of this inven' tion will becomereadily apparent from the following description read with reference tothe accompanying drawings in which:

FIG. 1 is a cross-sectional view of a gas laser according to thisinvention;

FIG. 2 shows a modified embodiment of the gas laser shown in FIG. 1;and,

FIG. 3 shows yet another modified embodiment according to thisinvention.

Referring to FIG. 1, a capillary tube 1 is provided, for example, ofquartz glass. A cathode 2 and an anode 3 are respectively arranged inbranch tubes 4 and 5 forming part of the capillary tube 1. The length ofthe capillary tube is greater than the distance between the two branchtubes. The branch tubes are fusedto an external tube 6 more or lesscoaxially arranged with the capillary tube ll. Windows 7 and 8 throughwhich light passes are provided at each end of the external tube,thereby tightly sealing the interior of the tube. The capillary tube 1and the external tube 6 are charged with CO or some other gaseous lasingmedium. The cathode and anode are connected to a power supply source 12comprising a D.C. source 9, a resistor for stabilizing the dischargebetween the cathode and anode and a trigger voltage source 11.

In the above arrangement, a D.C. voltage and a trigger voltage areapplied between the cathode and anode by the D.C. source 9 and thetrigger voltage source 11. As a result, a constant D.C. discharge isgenerated in the capillary tube 1, the discharge current beingmaintained at a value best suited for laser action. Further, since theimpedance of the path from the anode 3 to the cathode 2 via the spacebetween the external tube 6 and the capillary tube 1 is higher than thatof the path from the anode 3 to the cathode 2 via the interior of thecapillary tube 1, there is no discharge in the space between theexternal tube and the capillary tube 1.

Plasma is produced in the capillary tube 1 by the discharge and thegaseous medium is ionized. The plasma area P within the capillary tubesis indicated by crosshatching on the drawings. Laser action is carriedout by two reflectors l3 and 14 constituting a laser resonator.

In the case of the CO laser, the CO molecules are positively ionized andin the case of the He-Ne laser, for example, the Ne gas is positivelyionized. Hence, the ionized gases are attracted towards the cathode byelectro-phoresis. The ionized gas, upon reaching the cathode, isneutralized and then rapidly returned to the anode 3 via the pathbetween the tubes.

As a result, the gas pressure in the capillary tube remains constant atall times thereby, ensuring a stabilized laser output. Further, sincethe gas does not collect on the cathode, the amount of gas absorbed isminimal. Again, in spite of gas leakage through the capillary tube as aresult of the capillary tube being heated by gas discharge, the gaspressure in said tube remains perfectly constant, since the escaping gasis returned to the tube via the space between said tube and the externaltube. Consequently, the life of the gas laser accord ing to thisinvention is not curtailed.

In the embodiment shown in FIG. 1, the trigger voltage for triggeringthe discharge in the capillary tube is applied between the cathode andanode. As an alternative, however, it is possible to provide a triggerelectrode in the vicinity of the cathode or anode.

In the embodiment shown in FIG. 2, a capillary tube 21 is fixed to theexternal tube 22 by two members 23 fused to the external tube. Acylindrical cathode 24 is coaxially arranged in the capillary tube 21.An anode 26 is provided in a branch tube 25, forming part of theexternal tube 22, saidbr'anch tube being in the near vicinity of one endof the capillary tube 21. Since the impedance of the path from the anode26 to the cathode 24 via the area A in the capillary tube 21 is lowerthan that of the path from the anode via the area B between thecapillary tube 21 and the external tube 22, the discharge is generatedvia the area A by applying the D.C. and trigger voltages between theanode and cathode.

In the above embodiment, the gas ionized by the discharge is attractedtowards the cathode 24, where it is neutralized and then returned to theanode side of the external tube 22 via the area B. Further, since thegas escaping through the capillary tube wall permeates the area B andreturns to the capillary tube, the life of the gas laser as shown inFIG. 2 is not curtailed and the output of the laser is stable.

In the embodiment shown in FIG. 3, the capillary tube as shown in FIG. 1is cooled in order to increase the laser output. Common parts in bothfigures are numbered identically. A cooling tube 31 is coaxiallyarranged around the capillary tube l. Cooling water applied via an inletpipe 32 circulates through the cooling tube 31, the heated cooling waterdue'to heat exchange being forced out through outlet pipe 33. In thisway, the temperature of the plasma generating area in the capillary tube1 is lowered andthe laser output is increased.

Having thus described the invention with the detail and particularity asrequired by the Patent Laws, what is desired protected by Letters Patentis set forth in the following claims.

We claim:

1. A gas laser having an active medium of ionized gas comprising:

A. an external tube for enclosing the gaseous medium;

B. a capillary tube opened at both ends arranged about the lasing axisand within the enclosure of the external tube, there being an annularspace formed between said external and capillary tubes, said space beingin direct communication with both open ends of the capillary tube;

C. a cathode and an anode arranged for generating a ionized gasproducing D. C. discharge, said cathode and anode arranged with thelowest impedance path therebetween passing through a portion of saidcapillary tube less than the entire length thereof, such that an ionizedgas area shorter than said tube is produced within said tube, saidcapillary tube defining spaced openings such that the ionized gas uponreaching said cathode is neutralized and returned to said anode via thepath between said capillary and external tubes; and,

D. a laser resonator for carrying out laser action.

2. A gas laser having an active medium of ionizeed gas comprising:

A. an external tube for enclosing the gaseous medium;

B. a capillary tube opened at both ends arranged about the lasing axisand within the enclosure of the external tube, there being an annularspace formed between said external and capillary tubes, said space beingin direct communication with both open ends of the capillary tube;

C. two branch tubes connected with said capillary tube between the openends thereof;

D. a cathode and an anode for generating a ionized gas producing D. C.discharge, said cathode and anode respectively arranged in said branchtubes, the length of said capillary tube being longer than the ionizedgas produced in said capillary tube and such that the ionized gas uponreaching said cathode is neutralized and returned 'to said anode via thepath between said external and capillary tubes; and,

E. a laser resonator for carrying out laser action.

3. A gas laser having an active medium of ionized gas comprising:

A. an external tube for enclosing the gaseous medium;

B. a capillary tube opened at both ends arranged about the lasing axisand within the enclosure of the external tube, there being an annularspace formed between said external and capillary tubes, said space beingin direct communication with both open ends of the capillary tube;

C. a cooling tube arranged around said capillary tube for containingcooling water applied into said cooling tube;

D. a cathode and an anode for generating a ionized gas producing D. C.discharge, said cathode and anode arranged with the lowest impedancepath therebetween passing through a portion of said capillary tube lessthan the entire length thereof, such that an ionized gas area shorterthan said tube is produced within said tube, and such that the ionizedgas upon reaching said cathode is neutralized and returned to said anodevia the path between said cooling and external tubes; and,

E. a laser resonator for carrying out laser action.

4. A gas laser according to claim 3 wherein the gaseous medium includescarbon dioxide gas.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,781,708 Dated December 25. 1973 lnventofls) Noboru Henmi and HiromiKumagai It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

On the first page of the patent after the line listing the inventorsinsert the following:

-Assignee: Nihon Denshi Kabushiki Kaisha-.

Claim 2 Column 3 Line 28 Q --ionizeed-- should read --ionized--.

Signed and Sealed this eleventh 13%) 0f N0vember1975 [SEAL] Arrest:

RUTHC. MASON C. MWRSHALL DANN Arresting Officer (nmmisxiunvr of Patentsum] Trademarks FORM PO-IOSO (10-69) -gc 037e-p59 U.Sv GOVERNMENTPRINTING OFFICE: e 9 9 UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION Patent No. 3,7 ,7 Dated D e 25, 973

Inventor(s) Noboru Henmi at a].

n the above-identified patent It is certified that error appears 1below:

and that said Letters Patent are hereby corrected as shown Claim 2,column 3 line 28, "ionizeed" should read ionized Signed and sealed this25th day of June 19%..

(SEAL) Attest:

Attesting Officer USCOMM'DC 60376-P69 FORM PO-105O (10-69) w u. 5.GOVERNMENT PRINTING OFFICE: 1959 o-sss-3:u,'

1. A gas laser having an active medium of ionized gas comprising: A. anexternal tube for enclosing the gaseous medium; B. a capillary tubeopened at both ends arranged about the lasing axis and within theenclosure of the external tube, there being an annular space formedbetween said external and capillary tubes, said space being in directcommunication with both open ends of the capillary tube; C. a cathodeand an anode arranged for generating a ionized gas producing D. C.discharge, said cathode and anode arranged with the lowest impedancepath therebetween passing through a portion of said capillary tube lessthan the entire length thereof, such that an ionized gas area shorterthan said tube is produced within said tube, said capillary tubedefining spaced openings such that the ionized gas upon reaching saidcathode is neutralized and returned to said anode via the path betweensaid capillary and external tubes; and, D. a laser resonator forcarrying out laser action.
 2. A gas laser having an active medium ofionizeed gas comprising: A. an external tube for enclosing the gaseousmedium; B. a capillary tube opened at both ends arranged about thelasing axis and within the enclosure of the external tube, there beingan annular space formed between said external and capillary tubes, saidspace being in direct communication with both open ends of the capillarytube; C. two branch tubes connected with said capillary tube between theopen ends thereof; D. a cathode and an anode for generating a ionizedgas producing D. C. discharge, said cathode and anode respectivelyarranged in said branch tubes, the length of said capillary tube beinglonger than the ionized gas produced in said capillary tube and suchthat the ionized gas upon reaching said cathode is neutralized andreturned to said anode via the path between said external and capillarytubes; and, E. a laser resonator for carrying out laser action.
 3. A gaslaser having an active medium of ionized gas comprising: A. an externaltube for enclosing the gaseous medium; B. a capillary tube opened atboth ends arranged about the lasing axis and within the enclosure of theexternal tube, there being an annular space formed between said externaland capillary tubes, said space being in direct communication with bothopen ends of the capillary tube; C. a cooling tube arranged around saidcapillary tube for containing cooling water applied into said coolingtube; D. a cathode and an anode for generating a ionized gas producingD. C. discharge, said cathode and anode arranged with the lowestimpedance path therebetween passing through a portion of said capillarytube less than the entire length thereof, such that an ionized gas areashorter than said tube is produced within said tube, and such that theionized gas upon reaching said cathode is neutralized and returned tosaid anode via the path between said cooling and external tubes; and, E.a laser resonator for carrying out laser action.
 4. A gas laseraccording to claim 3 wherein the gaseous medium includes carbon dioxidegas.